Human immunodeficiency virus (HIV) infection of the central nervous system (CNS) results in progressive neurologic dysfunction in pediatric and adult acquired immunodeficiency syndrome (AIDS) patients. The identification of HIV markers within multinucleated giant cells structure derived from cells of the monocyte/macrophage lineage (including brain microglial cells) represents one of the major indicators of HIV CNS invasion. However, due to the limited sensitivity of the techniques utilized to detect viral markers and the refractile nature of neuroglial cells to productive HIV-1 infection in vitro, it remains possible that brain neuroglial cells amy also be infected in vivo with infection likely to occur as a restricted infection with low level viral gene expression leading to cellular perturbation and neuroglial dysfunction. These studies suggest the neurologic dysfunction involves the interaction of HIV-1 with target cells of both immune and nervous system origin that include monocyte/macrophage, microglial cells, astrocytes, and to a lesser extent, olligodendrocytes and neurons. Subsequent to viral entry, the outcome of HIV-1 infection in a given cell type within the immune or nervous system is critically dependent on cellular factors that interact with retroviral LTR sequences that are localized within the U3, R, and U5 regions of the HIV-1 LTR and that the level of expression is potently unregulated by the viral transactivator protein Tat. Furthermore, studies have also demonstrated that cellular factors may also regulate the level of LTR activity. As a consequences of cellular factor-mediated modulation of LTR activity, it is possible that cell-type specific factors may play a critical role in modulating viral activity in neuroglial cells. Therefore, the level of viral expression in the brain may not only be influenced by the cell type infected but also by the state of cellular differentiation and by extracellular signals. Based on these observations, we propose to characterize the neuroglial cell factors and viral sequences that may be involved in regulating HIV-1 LTR activity and viral gene expression in the CNS. The specific aims of the proposed studies are to utilize a series of cell lines and primary cell populations of immune and nervous system origin to (1) identify cis- acting sequences involved in regulating HIV-1 LTR activity utilizing transient expression assays; (2) characterize the contribution of selected cis-acting sequences to HIV-1 LTR activity in the context of infectious viral constructs; (3) characterize trans-acting factors participating in cell type-specific regulation of HIV-1 LTR activity in cells of human CNS origin and; (4) identify sequence variations in PCR- derived HIV-1 LTR clinical isolates which contribute to cell type- specific regulation of LTR activity in cells of human CNS origin. Characterization of the neuroglial cell populations may have direct bearing on our understanding of the neurologic dysfunction associated with HIV-1 infection in humans.